Sift flour and cornstarch into a mixing bowl. Set aside.

Beat sugar and butter with an electric mixer for 5 - 7 minutes, or until fluffy and pale. Add vanilla and mix to combine.

Add flour and cornstarch mixture and beat until dough forms.

Roll the dough out between two pieces of parchment paper to ¼ inch thick. Refrigerate for 30 minutes.

Preheat oven to 350º F. Line two cookie sheets with parchment paper. Set aside.

Using a 2 inches round cookie cutter, cut as many rounds as possible from the dough. Place them on cookie sheets.

Bake for 10 -12 minutes, or until light golden.

Remove baking trays from oven and let the cookies cool on the tray.

When the cookies are cool, spread half the cookies with a dollop of Dulce de Leche. Then sandwich with remaining cookies.